Rat parvoviruses are common infectious agents of laboratory rats. Infection is often asymptomatic, but severe disease can occur in fetal, suckling and juvenile rats. Parvoviruses also can interfere with research by distorting responses that require nucleic acid synthesis such as cellular immunity and can persistently infect cultured cells, but the course of infection in rats has not been established. Clarification of the pathogenesis, duration and transmission of parvovirus infection is essential for devising sound methds for detection, control and prevention. The proposed research will use a prototype parvovirus (rat virus) to determine: 1) the duration of infection (.i.e. does virus persist in rats), 2) factors that may influence the duration of infection, 3) correlations between duration of infection and rat-to-rat transmission of virus, and 4) if virus-free progeny can be derived from previously infected dams by simple quarantine methods. These objectives will be sought using a variety of modern techniques to detect persistent virus infection including: explant culture, nucleic acid hybridization in vitro and in situ, and enzyme immunohistochemistry. Studies of immunological factors will utilize T cell deficient (athymic) rats. The long-term objectives are to determine the mechanism(s) by which rat virus can persist in immune hosts.